Idiopathic intracranial hypertension (IIH) is a disorder of obese young women characterized by elevated intracranial pressure (ICP) of unknown cause. It affects at least 100,000 Americans and its incidence is increasing with the obesity epidemic. Because of pressure on the optic nerve (papilledema) about 10% develop blinding visual loss. We recently completed the Idiopathic Intracranial Hypertension Treatment Trial, a multicenter randomized, double-masked, placebo-controlled study of 165 subjects with IIH and mild visual loss. We showed that acetazolamide-plus diet was significantly superior to placebo-plus-diet for improving 1) perimetric mean deviation (PMD, a global measure of visual field loss), 2) papilledema grade, 3) quality of life (QoL) measures and ICP. Further, high dose acetazolamide (up to 4gm/day) was well tolerated. However, in subjects with moderate to severe visual loss, no intervention, neither medical nor the various surgical approaches, has been verified as efficacious by well-designed clinical trials. We will enroll 180 newly diagnosed IIH subjects with a PMD between -8.5 and -30 dB in at least one eye, as determined by automated perimetry. We will compare the efficacy of 1) maximal medical therapy (MMT), 2) surgical intervention with optic nerve sheath fenestration + MMT, and 3) surgical intervention with intracranial shunting + MMT using an intention-to-treat analysis. The primary outcome will be the change in PMD from baseline to 6 months in the eye with the best qualifying PMD. Secondary outcomes include: OCT measures; changes in papilledema grade, ICP; and QoL scores. We will investigate how interventions that purportedly lower ICP determine a) biomechanical changes of the optic nerve head and b) if retina ganglion cell layer thinning at baseline is associated with a poor visual outcome. We will follow subjects for at least two years to determine the long-term outcomes of these treatment strategies. The Neuro-ophthalmology Research Investigator Consortium (NORDIC) will provide the infrastructure and experienced leadership to conduct the proposed study, consisting of 41 sites, the Data Coordination and Biostatistics Center, three Reading Centers (under a Resource Center), and an Enrollment Center.